Radiation curable phase change gel inks may be used to form images on substrates in printing. The ink may be exposed to radiation to cure the ink. Exemplary radiation-curing techniques include, for example, curing using ultraviolet (UV) light, for example having a wavelength of 200-400 nm or more rarely visible light, optionally in the presence of photoinitiators and/or sensitizers, curing using thermal curing, in the presence or absence of high-temperature thermal initiators (and which may be largely inactive at the jetting temperature), and appropriate combinations thereof.
During this exposure, photoinitiator substances contained in the ink may be irradiated with the UV radiation, and the incident flux converts monomers in the ink into a cross-linked polymer matrix, resulting in a hard and durable mark on the substrate. For some applications, it may be desirable to spread or level the ink on the substrate before curing. Leveling can produce more-uniform image gloss and mask missing jets of print heads. Additionally, certain print applications, such as packaging, may benefit from having thin ink layers of relatively-constant thickness in prints.
UV curable phase change inks may have a gel-like consistency at ambient temperature. As UV gel inks are heated from about ambient temperature to an elevated temperature, they undergo a phase change to a low-viscosity liquid. These inks may be heated until they change to a liquid and then applied to a substrate. Once the ink contacts the substrate, the ink cools and changes phase from the liquid phase back to its more viscous, gel consistency.
UV curable gel ink images such as those formed by inkjet printers configured for radiation curable gel ink printing tend to display a non-uniform gloss. For example, such images may exhibit a “corduroy effect”, and/or may suffer from common inkjet image quality streaking caused by missing ink jets. To overcome such deficiencies, the ink may be thermally re-flowed before curing. While this technique may mask missing jets, resulting images may suffer from instability on smooth substrates and/or bleed-through or showthrough on porous substrates. Accordingly, it has been found that contact-leveling gel ink on a substrate by contacting a gel ink image with a contact member such as a leveling roll effectively spreads the ink before final cure to mask missing jets and/or improve gloss uniformity.